Regularly inspecting a turbine is necessary to reduce the chance of experiencing an unexpected failure. The frequency of turbine inspection is generally determined by the requirement that it should be such as required to maintain the equipment and to ensure its operating function. Normally a frequency of once per year is recommended.
Hydraulic turbines may be used to expand liquefied natural gas from a high pressure (typically between 40 bar and 150 bar) to about atmospheric pressure. Since the volumetric flow rates of the liquefied natural gas flowing through the turbines is of the order of 500 m3/hour, the size of such turbines is great.
Inspecting such a large turbine is very laborious, and associated with such an inspection is a loss of production of liquefied natural gas. On the other hand, there are huge consequences associated with a failure of a component of such a turbine.
Therefore there is a need for a simple method of monitoring the condition of a turbine, which results in a qualitative assessment of the condition. Based on this assessment it can be assessed whether inspection is warranted.